1. Field of the Invention
The present invention relates to testing a fiber link, and more particularly, to a technique for testing a fiber link in a communication system without interrupting service in the communication system.
2. Description of the Related Art
For a high capacity fiber optic transport system such as a synchronous optical network (SONET) or a dense wave division multiplexing (DWDM) system, quality or condition of all elements of a fiber link between terminals is very important. These elements may include optical fiber, connectors, splices, attenuators and other optical components. Fiber link degradation due to poor performance of one or more elements could cause service interruption. The condition of the fiber link in service is also important when service is being upgraded to a higher speed, for example, by utilizing additional wavelengths, and it is also desired to make such an upgrade without service interruption.
Current methods for testing a fiber link are not performed while normal communication signals are routed through the fiber link. To test a fiber link that is being used for normal communication, the communication signal may be switched to another fiber link, designated as a protection path, but such switching causes at least a short service interruption. If there is no protection path, and therefore no fiber link to which the communication signal can be switched, then there will be a relatively long service interruption. The service interruption is necessary in order to access one or both ends of the fiber link under test.
An alarm is an indication that a signal has failed, or that an optical power level is below an acceptable threshold. Conventional optical transport systems provide information and alarms by monitoring the optical signal power level. However, in a case of signal degradation, monitoring of received optical signal power cannot identify a cause or a location of the signal degradation. Consequently, further analysis of the problem or sectionalization of the system would typically require service interruption. A service interruption is also typically required in order to definitively determine whether a fiber can handle a particular set of wavelengths.
Consequently, there is a need for a technique for testing a fiber link in a communication system without interrupting service in the system.